Oxygen Adsorption on free and deposited Clusters

For many catalytic processes the adsorption and activation of oxygen is of major importance. Nano-particles (cluster) essentially differ in there properties from the well-known macroscopic environment. For example: metal cluster can act as semiconductors or even insulators.In the context of this work the chemisorption of oxygen on metal (Cu, Pd) and semiconductor clustern (Si) is studied. By means of anion photoelectron spectroscopy (PES) it could be shown that oxygen dissociates on small copper cluster anions. However, molecular oxygen forms an activated hyperoxide species on clusters consisting of 6 to 10 copper atoms.On small (1-3 atoms) palladium cluster anions oxygen adsorbs dissociatively. With increasing cluster size the influence of oxygen bonding on the forming conduction band of the palladium cluster is fading. However, a definite answer on the chemisorption of oxygen on the larger palladium clusters is not possible up to this point.Stable clusters can be used as building blocks for new cluster materials. An example is the Fullerit, a solid state formed of C60 clusters. In the present work, "magic" Si7-clusters on surfaces were examined, in particularly the suitability of these cluster as components of a new solid body. The clusters are produced in a magnetron sputter gun, separated and soft landed onto different surfaces.By means of X-ray electron spectroscopy (XPS) first indications are found, which point to the fact that Si7 on surfaces is very stable in relation to chemical reactions and not likely to merge with neighboring clusters. In contrast, deposited silicon clusters with 8 or 9 silicon atoms exhibit a high reactivity towards oxygen. Results which point in the same direction are obtained by Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS). In addition theoretical simulation are carried out